1. Field of the Invention
The present invention relates to selectively enhancing corrosion protection of fabricated metal structures and, more particularly, to methods of applying a protective coating to metal parts using kinetic spraying.
2. Background Art
xe2x80x9cGalvanizingxe2x80x9d refers to a broad category of surface coating processes wherein zinc or zinc-rich alloys are deposited on the surfaces of steel sheets or fabricated metal parts. In the automotive industry, as well as other industries, the use of galvanizing for corrosion protection of steel is ubiquitous. The International Zinc Association estimates that worldwide annual usage of zinc for this purpose exceeds 3 million metric tons. Coils of steel, for example, are frequently provided with galvanized coatings through processes such as hot dipping, electro-galvanizing or galvannealing. Such coil-coated steel is subsequently formed into products such as automobile bodies, architectural materials and other products for commercial and household use. The coil-coated steel can be further finished by additional treatments that include phosphating electrophoretic coatings.
Even with the application of galvanic protective coatings to steel, corrosion may still occur, particularly in localized regions where the mechanical integrity of the coatings may be compromised by such processes as joining, cutting, forming or any other manufacturing process which may diminish the capability of protective layers to provide protection to the steel sheet. Hence, to compensate for these potential deficiencies produced during the manufacturing of the galvanized metal parts, post processes, such as painting or phosphating have been utilized.
Fabricated metal parts suffer from corrosion resistance problems as well. For example, metal fuel tanks have extremely high corrosion reliability requirements. Currently, only metal fuel tanks are capable of meeting the most stringent regulatory requirements for low emission vehicles. Corrosion of metal fuel tanks, however, is a critical concern since a single pit can lead to fuel leakage and attendant system failure. Current practice for corrosion prevention of steel fuel tanks involves use of electro-galvanized (e.g., Znxe2x80x94Ni alloy) sheet steel as the base metal, combined with an aluminum-rich, epoxy paint. At the tank seam element as well as attachment points for inlets and fuel pump, the corrosion performance can be diminished due to possible inherent defects associated with the manufacture of the tank.
There exists a need in the automotive industry, as well as other industries, for a simple, low-cost method for selectively applying a protective coating to metal parts for corrosion resistance of localized regions that may or may not have an existing protective coating. This type of method would be especially advantageous where an original coating protection has been compromised by various manufacturing processes such as cutting or welding. Furthermore, there is a need to provide for enhanced corrosion protection at localized regions of fabricated metal structures that may or may not have an existing protective coating.
The present invention is related to methods for selectively enhancing corrosion protection of fabricated metal parts.
One preferred method of the present invention involves selectively enhancing corrosion protection of a fabricated metal part. The preferred method includes providing a non-galvanized metal sheet to be processed to form a fabricated metal part; selecting a localized region on the non-galvanized metal sheet; roughening the localized region for acceptance of a protective coating; applying a protective coating to the localized region; and fabricating the non-galvanized metal sheet into a fabricated metal part.
If not treated with the protective coating, the localized region becomes a post-fabricated area particularly susceptible to corrosion. Upon applying the protective coating to the localized region, the post-fabricated area is particularly resistant to corrosion. The protective coating is applied by a device capable of impact fusion of solid metal particles. The corrosion protection of the post-fabricated area is enhanced by the selectively deposited protective coating. The protective coating may be a galvanized coating. However, non-galvanized coatings can be utilized as long as corrosion resistance is enhanced (viz. oxidative or high temperature corrosion protection).
In another preferred embodiment, a method includes providing a galvanized metal sheet to be processed to form a fabricated metal part; selecting a localized region on the galvanized metal sheet; applying a supplemental galvanized coating to the localized region; and fabricating the galvanized metal sheet into the fabricated metal part. The application of the galvanizing coating forms a galvanic layer on the surface of the prefabricated metal sheet. If not treated with the supplemental galvanized coating, the localized region becomes a post-fabricated area particularly susceptible to corrosion. Upon applying the supplemental galvanic coating to the localized region, the post-fabricated area is particularly resistant to corrosion. The corrosion protection of the post-fabricated area is enhanced due to the selective application of the galvanic coating. The galvanized coating is applied by a device capable of impact fusion of solid metal particles.
One preferred method includes selecting a localized region on a fabricated metal part; roughening the localized region for acceptance of a protective coating; and applying a protective coating to the localized region. The protective coating is applied by a device capable of impact fusion. According to this method, the fabricated metal part is treated. For example, an element on a fuel tank seam may lack corrosion protection. The method contemplated enhances or restores corrosion protection to the localized region defined by the weldment.
These and other advantages, features, and objects of the present invention will become more apparent to those of ordinary skill in the art upon reference to the following description.